<!DOCTYPE html>
<html lang="en">

<head>
  <meta charset="UTF-8">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <title>Document</title>
  <!-- 引入vue -->
  <script type="text/javascript" src="../js/vue.js"></script>
</head>

<body>

  <div id="root">
    <h2>今天天气{{info}}</h2>
    <button @click="changeWea">切换天气</button>

  </div>
  <script type="text/javascript">
    Vue.config.productionTip = false //阻止 vue 在启动时生成生产提示。、
    const vm = new Vue({
      el: '#root',
      data: {
        isHot: true,
      },
      computed: {
        info() {
          return this.isHot ? '炎热' : '凉爽'
        }
      },
      methods: {
        changeWea() {
          this.isHot = !this.isHot
        }
      },
      watch: {

        // 正常写法
        /*   isHot: {
            // immediate: true,
            // deep: true,
            handler(newValue, oldValue) {
              console.log('ishot已修改', newValue, oldValue);
            }
          }, */

        // 当配置对象中只有handler时，可以采用简写模式
        /* isHot(newValue, oldValue) {
          console.log('ishot已修改', newValue, oldValue);
        } */
      }
    })

    // 正常模式
    /*  vm.$watch('isHot', {
       // immediate: true,
       // deep: true,
       handler(newValue, oldValue) {
         console.log('ishot已修改', newValue, oldValue);
       }
     }) */

    // 简写模式
    vm.$watch('isHot', function (newValue, oldValue) {
      console.log('ishot已修改', newValue, oldValue,this);
    })
  </script>
</body>

</html>